1. Field of the Invention
The present invention relates to a sound field controller for reproducing sound effects for use in audio equipment or in audio-visual (AV) equipment.
2. Description of the Related Art
In recent years, as VTRs (video tape recorders) have become a common household item, a large-screened display and a sound reproduction system giving a sense of presence are desired to enjoy music recorded on recording media or programmed in softwares as well as movies on video tapes at home, thereby giving rise to the requirement of corresponding hardware development.
A conventional sound field controller will be explained with reference to the figures.
FIG. 20 shows a hardware block diagram indicating the structure of a conventional sound field controller. Stereo-audio signals are input via input terminals 1 and 2 to the sound field controller. The conventional sound field controller comprises a multiplier 62 for multiplying an input signal by -1, an adder 63 adds the input signals, a delay circuit 64 for delaying the input signal by a predetermined time, adders 12-5 and 13-5 for adding the input signals, a multiplier 65 for multiplying the input signal by -1, and speakers 14 and 15 for reproducing the signals and playing the sound for a listener 16 facing the speakers 14 and 15. ML(t) and MR(t) represent a Left-channel signal and a Right-channel signal of the stereo-audio signal respectively, and t represents a continuous time, ML(t) and MR(t) being functions of time. .tau..sub.3 represents the delay time in the delay circuit 64.
The operation of the conventional sound field controller configured as above will be explained with reference to FIG. 20.
ML(t) is applied through the input terminal 1, and MR(t) through the input terminal 2. Each of the signals ML(t) and MR(t) thus input is divided into two parts, so that MR(t) is inputted to the adders 63 and 12-5 and ML(t) to the multiplier 62 and the adder 13-5. The multiplier 62 multiplies ML(t) by -1, and the result -ML(t) is applied to the adder 63. The adder 63 adds MR(t) and -ML(t) to produce the result MR(t)-ML(t), which is applied to the delay circuit 64. The delay circuit 64 delays MR(t)-ML(t) by fixed time and produces MR(t-.tau..sub.3)-ML(t-.tau..sub.3). The output signal of the delay circuit 64 is divided into two branches of signal. One signal is applied to the adder 12-5, and the other signal to the multiplier 65. The multiplier 65 multiplies MR(t-.tau..sub.3)-ML(t-.tau..sub.3) by -1, and the result of multiplication, -(MR(t-.tau..sub.3)-ML(t-.tau..sub.3)), is applied to the adder 13-5. The adder 12-5 adds MR(t) and MR(t-.tau..sub.3)-ML(t-.tau..sub.3), and the sum MR(t)+MR(t-.tau..sub.3)-ML(t-.tau..sub.3) is produced and output from the speaker 14. The adder 13-5 adds ML(t) and -(MR(t-.tau..sub.3)-ML(t-.tau..sub.3)), and the result ML(t)-(MR(t-.tau..sub.3)-ML(t-.tau..sub.3)), is output from the other speaker 15.
In this process, the signals MR(t-.tau..sub.3)-ML(t-.tau..sub.3) and -(MR(t-.tau..sub.3)-ML(t-.tau..sub.3)) in antiphases each other are mixed with the respective input signals and reproduced from the two speakers respectively, with the result that a sound field is generated with an non-identifiable localization of the sound image (or, the subtracted signals cancel the crosstalks thereby to yield the feeling as if the right and left signals are reproduced from outside of the two speakers). By adjusting the mix balance with ML(t) and MR(t) which are unprocessed direct sound signals, a sound field is produced with expansion and presence (i.e. the sound is produced with giving a sense of expansion of the sound and a sense of presence to a listener). For example, a sound reproduction giving a listener the illusion of being in the same room (such as a concert-hall) as the original source of sound rather than in the room with the sound reproducing system is a sound reproduction with presence.
In the above-mentioned structure, however, adjustment of the sound field is performed by the mix balance between the antiphased sounds and direct sounds. Thus, if the antiphased sounds are relatively small, that would reduce the effect, while if the antiphased sounds are made larger to emphasize the effect, that would strengthen the antiphased sound, bringing about an uncomfortable feeling to the listener. Further, in the case where the input signal is a voice-sound signal, the conventional structure has a problem that the voice component is reduced when the difference signal of the input signal is added to the input signal, thereby the reproduced voice sound being ambiguous.
FIG. 21 shows a block diagram of a conventional sound field controller capable of sound reproduction with presence.
In FIG. 21, input terminals 1 and 2 are supplied with a signal ML(t) to be reproduced from the left side channel (Lch) as viewed from the listener 16 and a signal MR(t) to be reproduced from the right side channel (Rch) as viewed from the listener 16, respectively. These input terminals 1 and 2 are connected to speakers 74 and 75. These two signals are added to each other by an adder 72 at a predetermined ratio, and then applied to a speaker 76 arranged at the front center of the listener 16.
Also, the two signals ML(t) and MR(t) are processed and applied to a surround signal generation circuit 71. The surround signal generation circuit 71 generates a signal S(t) called a surround signal indicting a reverberation and/or a reflection, which is caused when the input signal is output from the speakers in an ordinary room. The surround signal S(t) produced by the surround signal generation circuit 71 is applied to two speakers 69 and 70 arranged on the left and right sides of the listener 16. The signals ML(t) and MR(t) normally represent what is called the stereo signal, or main signals as compared with the surround signal S(t).
In the structure shown in FIG. 21, the 2-channel (2ch) signals ML(t) and MR(t) normally reproduced from the VTR, etc. are applied to the surround signal generation circuit 71. The surround signal generation circuit 71 generates the surround signal S(t) of the reverberation or the reflection. The main signals ML(t) and MR(t) are reproduced from the speakers 74 and 75 respectively, and the surround signal S(t) is divided into two parts and reproduced from the speakers 69 and 70. Also, the main signals ML(t) and MR(t) are added at a predetermined ratio by the adder 72, and the resulting sum signal is reproduced from the speaker 76.
As compared with a 2ch stereo reproduction system generally using two front speakers, the above-mentioned audio reproduction system allows a sound reproduction with good presence by reproducing sounds that had been audible from the front only or sounds that could not be heard, from the sides or behind as a surround sound. Further, since the main signals ML(t) and MR(t) are added at an appropriate level and reproduced from the center speaker 76, the front sound image is definitely localized.
In the above-mentioned structure, however, additional speakers arranged on the side or behind for reproducing surround signal are required as well as the space for accommodating the speakers.
In view of the problems of the conventional sound field controllers described above, the object of the present invention is to provide a sound field controller having a simple structure which is capable of unambiguous reproduction of a sound signal with presence and natural expansion.
Another object of the present invention is to provide a sound field controller for reproducing the sounds including the reflected and/or reverberation which are audible as if they are from positions other than the reproduction point of the speakers, thereby making possible a sound reproduction with presence without using any additional speakers on the sides or behind the listener.